This invention relates generally to a soil gas monitoring system and method and, more particularly, to an essentially passive, leak detection apparatus and method which relies primarily on diffusion to move a predetermined tracer from the leak point to the monitoring point for detecting fluid leaks from subsurface storage tanks such as buried gasoline or natural gas storage tanks which are monitored on a substantially regular schedule to test subsurface tank integrity even though no evidence indicates that a leak may exist.
The prior art is replete with systems for detecting leaks from liquid storage tanks. Some liquid leak monitoring systems utilize tank liners and sensors to detect leaks of the stored liquid or gaseous product. Unfortunately, installation of such a system at an existing service station or the like would require the digging out and removal of the existing subsurface tanks, thus resulting in extremely high installation costs and a disruption of the service station operation. Other devices that sense liquid level in the tank often require the tank to be out of service for 12 hours or more.
In other known underground liquid monitoring systems, monitoring points are established at locations lower in elevation than the buried tank and directly in the path of escaping liquid. Such systems often take the form of monitoring wells at the water table surface and usually require substantial digging. Unfortunately, such systems have a low probability of success, and leaks are generally only detected after a large amount of liquid product has escaped.
It is a standard in the oil industry to employ pressure test methods to detect leaks in buried tanks. However, such methods are usually only employed after a leak is suspected and not on a regularly scheduled or periodic basis. Such tests are very expensive (believed to cost $4,000 to $5,000 per test), and they interrupt normal operation of the tank. As a result, pressure testing is not performed on a frequent or routine basis.
Therefore, there is a long-felt and unfilled need in the prior art for a relatively low cost method and apparatus for detecting gas leaks in underground or subsurface gasoline or natural gas tanks by a monitoring system which enables leak checking or testing periodically or on a regular schedule, which detects even relatively small amounts of escaped gas or gasoline, and which does not require extensive digging or the disruption of normal service station operation.